The plural form of the noun “mouse” when referring to the animal is “mice.”
“Mice” is an irregular plural inherited from an older pattern of Germanic vowel change. In Old English, the singular was “mūs” and the plural was “mӯs”; over time, these developed into modern “mouse” and “mice.” The vowel change is known as an umlaut, in which a sound in a following syllable influenced the earlier vowel.
Most English nouns form plurals by adding “-s” or “-es,” as in “cat” and “box,” so “mice” must simply be learned as an exception. “Mouses” is not the standard plural for the animal, although “mouses” can sometimes appear in technical discussions of computer devices. The computer term also commonly uses “mice,” creating a playful connection between rodents and pointing devices.
A mouse is a small rodent, and the word can describe several species, not only the common house mouse, Mus musculus.